Browsing by Author "Labuschagne, Casper"

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    An investigation into source and distribution of bromoform in the Southern African and Southern Ocean Marine boundry layer
    (2014) Kuyper, Brett; Reason, Chris; Waldron, Waldron, Howard; Palmer, Carl J; Labuschagne, Casper
    Bromoform is a climatically important atmospheric trace gas. It is released by macro- and microalgae into the ocean, and rapidly transferred to the atmosphere, where bromoform undergoes rapid photolysis yielding bromine radicals. These bromine radicals are known to participate in catalytic destruction of ozone at all levels throughout the atmosphere. This is especially important in the lower stratosphere. This destruction of ozone results in changes in the oxidative potential and decreases the greenhouse effect of the troposphere. A task-specific gas chromatograph with electron capture detector system, developed in-house, was used for the separation and quantitative detection of bromoform mixing ratios from environmental air samples. A custom thermal desorption unit was designed and built for use in this system along with a graphical user interface for the real-time collection and display of data. A limit of detection of 0.79 ± 0.09 ppt, with an overall precision of 12.7 % was achieved with this GC system and method. The quantitative detection of bromoform mixing ratios was made at the Cape Point, Global Atmospheric Watch station over a one month period in early spring 2011. Bromoform mixing ratios detected ranged between 2.29 and 84.7 ppt with a mean of 24.7 ppt. These mixing ratios appear to be generally elevated compared to previous studies, however, were still within the maximum values published. Local kelp beds around Cape Point and possibly anthropogenic inputs from Cape Town are likely to have been the dominant source of bromoform measured there, caused by changes in wind speed. A series of experiments were performed to explore the role of the bromoperoxidase enzyme in providing antioxidant protection in two diatom species (Phaeodactylum tricornutum and Chaetoceros neogracile_cf ) under different oxidative stresses. Carbon dioxide and nitrate limitation were induced as oxidative stresses. The mean per cell bromoform concentrations during the growth phase of the carbon limitation were 2.73 x 10¯¹⁷ and 8.68 x 10¯¹⁸ mol cell¯¹ for C. neogracile_cf and P. tricornutum, respectively. This decreased to 2.94 x 10¯¹⁸ and 3.87 x 10¯¹⁸ mol cell¯¹ during the limited phase. Bromoform production decreased to zero for P. tricornutum during the nitrate limitation. These experiments suggest that in these species bromoperoxidase is not utilised as an antioxidant pathway when under these nutrient limiting conditions.
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    Variations of the chemical characteristics and source regions of aerosols at the Cape Point GAW station
    (2022) Spence, Kurt; Altieri, Katye; Labuschagne, Casper
    Nitrogen is an essential component for life. The natural nitrogen cycle has been greatly disturbed by the production of fertilizer and use of fossil fuels, such that it has doubled the amount of reactive nitrogen (Nr) produced globally. Excessive additions of Nr to the environment can have negative effects, including eutrophication, loss of biodiversity, enhanced greenhouse gas emissions, acidification, increased tropospheric ozone, and damage to human health. Excess ammonia (NH3) and nitrogen oxide (NOx) emissions lead to increased aerosol loading via secondary aerosol formation processes. Increased aerosol loading has impacts on the climate and on human health. Furthermore, the aerosols formed from Nr from continental sources can get deposited to the open ocean, which is usually nitrogen limited. Knowing the concentrations of different aerosol species from a pollution free environment, such as the remote open ocean, can give insights into the natural preindustrial conditions and be used as a baseline for looking into the impacts of anthropogenic activities. This thesis focuses on establishing the Cape Point Global Atmosphere Watch (GAW) station as a site for collecting aerosol samples from pristine marine air masses. The use of a tower site allows for high temporal resolution sampling across multiple seasons and years, which is logistically difficult when relying on ship-based sampling of pristine marine environments. Results are presented from the chemical composition analysis of aerosols sampled at the Cape Point GAW station, including comparisons of two different aerosol sampling systems (tall-tower PM10 and ground-based sizesegregated). Furthermore, the installation and testing of a sector-controlled sampling system designed to reduce continental influence on samples is evaluated. Air mass back trajectories and radon (222Rn) concentrations were used to classify the air masses of each aerosol sample as either marine, modified marine, or continental. We found that continental samples had elevated concentrations of NH4 + , NO3 - , and non-sea-salt SO4 2- , whereas the marine samples had elevated concentrations of Cl- , and Na+ , as expected. A comparison of the tall-tower PM10 and ground-based size-segregated sampling systems showed that the ground-based sampler measured higher concentrations of coarse mode aerosols. This is attributed to the settling of large aerosols within the long sampling intake tube from the tower sampling system. The sector-controlled sampling system based on wind speed and direction was able to remove some of the influence of continental air masses, however some continental influence could not be avoided as the continental air masses circulated over the ocean before being sampled from the marine sector. This system could be improved by having additional cut-off limits defined for sampling, such as particle number, black carbon, or carbon monoxide (CO) concentrations.